Since when did “common sense” have anything to do with CG regulations?
With regard to the idea that a 1AE being able to cover all the lower licenses, while that might be a regulatory possibility in that a 1st might be able to obtain the paper just by asking, as a hawespiper who has worked steam and motor in every position from wiper to unlimited chief on everything from tugs to tankers and fish factories, the concept is flawed.
Unless the 1st or 2nd has actual experience with the type of machinery found on smaller vessels (DG maintenance doesn’t count all that much) they will be crippled when it comes to the peculiarities of small vessel plants and operations. That doesn’t do anyone any favors.
I would prefer to see licensing include “type ratings” or something of that order so that the person in charge of a vessel and its machinery have actual operational experience with the machinery under his control.